Please -- let me welcome you to the forum. Cavalier's are among my favorite dogs on the planet.
To do *tempoarily* as a stopgap measure until the vet comes back? My choice would honestly be to go to another vet. For good reason ...
What are the symptoms? Just *trying* to urinate more than normal?
If *YOU* have ever had a uti you will know they can be excruciatingly painful -- you feel like you have terrible bladder pressure and *must* be able to go ... but then when you try you **can't** go (and it is SO painful and the burn is terribly deep). So particularly if you see her try to squat ... move a few more paces and try again and again ...
Go to another vet!!
The more they TRY to pee they will actually bruise the kidneys and will begin to pee blood. THAT can actually be a veterinary emergency. And honestly? for ME that is pretty tantamount to an emergency anyway simply because the pain can be so severe -- far more than she can communicate to you.
To explain -- cranberry does *not* fight infection. Not like an antibiotic will 'fight' (kill) bacteria. Cranberry is largely glucose -- and that glucose will bond with infection cells in the bladder. Then it actually helps make the infection cells too slick to *stick* to the urinary tract.
However -- if you have an already established infection (which is what it sounds like) then you're past that point -- the infection is already IN the urinary tract. It may help mildly to acidify the urine which may help it not burn quite so much. BUT *most* dog UTIs are a product of urine that is too alkaline ... but as Jennie rightly says ... not all dog's urine IS too alkaline and in that case you don't want to make it worse.
This usually isn't difficult to diagnose -- and honestly I would NOT wait for Monday -- this is painful!!!!! -- more than I can communicate to you if *you* have never had one.
Please call another vet near you -- explain that your vet is on vacation but your Cavalier is exhibiting signs of a pretty severe infection (and what you are describing DOES that -- with many dogs that's ALL the sign you will get prior to blood!) -- Honestly I would simply GO to another vet in the morning and ask to be treated. You don't have to go to them forever -- but getting treatment for this is important.
The other thing I'm going to put in your ear has to do with the fact that this is a Cavalier.
The urinary tract is connected to the bladder and kidneys. If there is in infection in the urinary tract is can easily back up all the way to the kidneys and suddenly you have a NASTY infection that can be difficult to resolve.
This is a Cavalier King Charles Spaniel -- they are quite predisposed to heart problems (I'm sure you're aware it's part of the breed to have a huge incidence of heart murmurs).
ANY time you put a load on the kidneys -- that means that the kidneys can't process and purify the blood the way they *ought* to. THIS then stresses the heart.
If your dog is at all *prone* to UTIs -- man, I would not waste time. I would get that treated in a heartbeat and if it IS something she gets "occasionally" all the way to "frequently" I would not just have them do a strip test -- I would ask for them to do a sterile draw and send it to a lab for a culture and sensitivity and MAKE SURE that the antibiotic given is the absolute right one to kill this infection.
I'm not trying to be a pain -- this is your first post so I don't know you at all. But **just in case** I wanted to warn you. You seem well aware of the symptoms of a UTI and sometimes that is because a dog has had them 'before'. Unfortunately some vets will just treat over and over and over with antibiotics without question -- without making SURE that this infection is totally and completely GONE.
When there is long term inflammation in the urinary tract you can wind up with kidney problems and early renal failure.
See that cute little cocker in my signature? Billy had a horrible disease called IMHA (Immune-mediated Hemolytic Anemia) 4 years ago -- in the process of treating that he had to take a drug that was hard on his kidneys. He also had to take huge steroid-like drugs to suppress his immune system.
He had "frequent" UTIs -- and despite the fact that I was "on it" ALL the time -- I never allowed the inflammation to go unchecked and I kept him on D-Mannose (which is better than cranberry) to help prevent the infections from recurring.
BUT DESPITE THAT -- we *know* we have some renal damage. Thankfully (maybe because I'm so anal about this stuff *sigh*) he's not doing badly -- but he sure could have. so unfortunately I know more than the casual owner about this stuff -- so I'm not trying to be a pain ... really I'm not. Just trying to help.
As I said -- let me welcome you to the forum. We surely do LOVE pictures and I hope this doesn't cause you a huge problem. Good luck!