toy poodles estrus cycle

Question
I'm dogsitting my brother's toy female supposedly so she can skip a breeding cycle. I have had her for 7 days and still no sign of estrus. She will be 3 yrs old next month and has had three litters. My brother figured her estrus 6 months from the last one. She has had a litter in between. Are we figuring the time correctly?  

Answer
You cant set a clock by them.  Most females arent that regular.  If she had a litter then that could have thrown her cycle way off.  Even if she has never been off before.  She will bleed for a week before she will even accept the male you will know at that time she is in heat and then you can bring her to your house.