It doesn't look like a bite. Does it feel like a blister, soft and squishy? That is all that it looks like to me. I would probably not take her to the vet just because of that either, but I won't try to talk you out of it. I do think if you can either email the pic or fax it to the vet, they might be able to relieve your worries without a visit.
I might just leave it alone for a week and see what happens to it on its own. I would lance it and add the neosporin
only if the vet thinks that is the thing to do. Thing is, bodies make those nice little blisters to let things heal with a good protective covering. This one does not look like it is filled with pus (infection). I know it has a yellowish tinge, but there is no redness in the area and it doesn't look gross (technical medical term
) It looks like most blisters which are full of a clear liquid that cushions the site, allowing it to heal in an enclosed sterile environment. Lancing it can unnecessarily allow bacteria in. I would only lance a blister if it is too large, causing discomfort or restricting movement, or looking infected, which this one is not.
Wanted to add that blister could be caused by many different things. It doesn't look like a place where friction would cause it, but maybe even a little urine left there could have irritated the skin. Other contaminants could have gotten there, anything from a household cleaner to sap from a weed or plant. Just ideas.....