
10 is the usual number, though I have had some with with 9 and one transposed non functional one next to the opposite rear one. One of mine has just 8 evenly paired with the two smallest front ones near the armpits missing.
It's also not unusual in some large breeds to have more, often small non functioning ones.
If a litter is small not all nipples may be used, or used little and remain small, but might come into use if there is larger litter another time.
If she hasn't been spayed it is best to get this done about 12 weeks after the pups were born so that it is not too close to when her next season is due (when there is increased blood supply in the area making spaying less straightforward), but long enough for milk to dry up fully.
EDIT:
Just realised you have had her since march so pups would have been born January and her season would have been in November, so she will have had a season since with you (May onwards)? Or was she spayed when you got her? If she was not spayed mid cycle, it might explain why her glands are taking a long time to return to normal as spaying during a time when a bitch still has milk can prolong things. If your talking just the nipples, they will never be pre pregnancy size again but should reduce in size often becoming flatter with time, and reduction in female hormones.