Hi and welccome,
Poor puss, she's obviously looking for food and comfort from you. Presumably you've asked round the neighbourhood whether she belongs to anyone? It may be worthwhile following the Found cat advice in the lost and found section we have here and posting in there, and try a paper collar to see if anyone claims her. But it may just be that she's a stray or just dumped. I'd try all the rescues listed on Cat Chat, even post there on the forum in Lost and Found section. If rescues are all full (which is likely as it's kitten season) you ought to get her on a waiting list, obviously if she's pregnant some rescues may prioritise her, hopefully but it's odd the vet didn't notice that, or ask for a direct homing where they source the home but you care for her just until then. It would be kind if you could provide her some food until then though.