
Hi Paul
If you haven't noticed any sign of bleeding or swelling of the vulva previously, then check her nipples. If these are prominent then in all likeliehood she has had a season (of sorts) possibly a 'silent season' where there is no blood show. If the nipples are not prominent and her vulva pre-pubescent size then she has yet to have a first season. When this happens neither the teats nor vulva return to quite so discreet a size as before.
All that aside, if your still have resident males then their behaviour towards her and interest in her would very definitely have alerted you to what was happening. If you intend to keep her entire, then I suggest you go onto Amazon and buy "The Book of the Bitch" which will be an invaluable guide to you for quick reference purposes and more :)
In the meantime don't be too concerned - one of my girls didn't come in until 21 months - unusual for her dam's line but obviously normal for her :) Ask your breeder what is the normal time span for her bitch line and it may give you some idea of what to expect.
Mother Nature takes care of the timing of these things so irrespective of your friend's bitch being in season it is less likely to affect your own girl. In multi bitch households it can sometimes mean that bitches over time synchronise their cycles (not that it's ever happened with mine ;) ) but I don't think a random short term visit would have any such result with your girl so really just a waiting game unless you believe on examination that you've missed the event (which TBH seems unlikely :) ).
regards, Teri