Heat Questions...

Okay - friends of mine finally found the perfect dog for them and of course yesterday afternoon she came into heat. *shaking head*  They are fully prepared to "foster" her until her spay.  She's the smallest lab I've ever seen (when she sits her head is just above knee height) and she's about 1.5yrs.  She was a surrender - but she has been wonderful with their little boy.  (We spent 2+ hours there over yesterday and today to make sure she would be okay.)
 
They had adopted a different dog - but he did not like kids and had to go back.  He's since been adopted into a family with kids that are away at school and much older! Yippee!!  Here's the thread: [linkhttp://forum.dog.com/asp/tm.asp?m=220565]http://forum.dog.com/asp/tm.asp?m=220565[/link]

So - she won't be able to be spayed for 3 weeks and my question is what should they expect from her?  Should they expect any behavioural changes over the next couple weeks?  They have a secure fenced yard and I've sort of explained what I know about males seeking her out.  Is there anything else they should know?