I've experienced this scenario before a few times only on a larger "silver" scale and looking back on it I wish I would have brought it to the attention of the manager or president(whoever is the highest available authority) like many on this site had told me to do.
I had NOTHING to lose but a LOT to gain,I just didn't have the nerve at the time and now that I feel I have the courage it is too late,the coins are long gone and I regret not doing anything about it at the time.
Now whenever I find halves with the tellers they seem to be friendly but no silver

.Plenty of '71-present though.
I have no problem with tellers pulling silver from loose change they receive,(I would do it myself if I worked at a bank),but when they have it visible to the customer and when asked for it the they get rude and say it's theirs,well that is too much and the should have to sell it to the customer as that is their job-to handle coin/currency-not to search coins and taunt people by leaving it in plain view and being rude when asked about it.
For all of us and for YOURSELF go back and see if they are still there(probably are) and ask for them again as if it is the first time and when you get a rude response,bring up the tone of your own voice(not yelling) but assertive and you will get the manager over there and you may get the silver,at the very least you can see her get a tongue lashing from the manager for causing upset in the bank and making people unhappy.
That alone would be worth it to me even if she got to keep the coins. :PGood luck.