It's most likely that she didn't know. It doesn't help her, either, to lead you up to that purchase point, only to have it fall through.
However--and I don't know the procedures in Pennsylvania--there should have been a review period for the condo documents. It's a contingency that likely was in your offer--that the contract was contingent upon receipt and approval of condo documents. Usually that occurs pretty early in the entire process. The condo documents should state, for instance, that dogs aren't allowed. The condo documents are also important for financial reasons--to see if the condo is financially stable and well-managed.
It's difficult to say that "she should have known." And, frankly, if she'd earlier sold a unit there to someone with a cat (and assuming cats are permitted), then it'd be understandable if she assumed that pets were permitted. But--as I said above--if you asked, she should have been very careful in her answer. I'm guessing--just guessing--that she assumed they were permitted and that you may not have asked. Again, there was no advantage for her in helping you make an offer, order an inspection, and so on if she'd known that your dog wouldn't be allowed.
Hope that helps.
Even better, if you are selling a property that is a condos or has a home owner association, the seller could leave the rule/regs on the table for a buyer to read thru if they are interested. This avoids the situation you are in.
It is impossible for an agent to know all the regulations (CCRs) for every condo complex. Even listing agents may not know, or could apprise the buyer and buyer's agent erroneously. This is why it's important to have the HOA documents front and center as part of the disclosures.
On the other hand...no one should ASSUME anything, particularly on the subject of pet restrictions.
We have a situation where a property was built as a rental complex where in they allowed pets. But once it was converted into a condo complex, the new rules changed the pet restriction to only 1 pet, and under 25 lbs. However, they grandfathered the folks who already lived in the complex, and some of them had big dogs, and sometimes more than one at a time. New buyers couldn't understand why the discrepancy.
Good luck to you...