Got one female dog in heat! when can I get her spayed?

I jus rescued a male dog. I already have a female dog, she is 2 yr old. both are small dogs. I was saving up money to get female one spayed. it costs about $310 for to get deed. I finally have the money, but she has gone in heat now. now I m trying my level best to keep them seperately. the issue is that they might be messing up before since they were playing in backyard for last couple of days. now I came to know about her being in heat just two days before.before that she was normal. the bleeding already started. she is foxy jack rusell terrier. so how long she will in heat and when is the best time to get her spayed? it sher second time around, but I forgot how the first one went. Now having male dog around. I just wana get her spayed as soon as I can.