Can you spay (spayed,Neuter) a female dog that has just had first "encounter" this evening?

Friend gave me her female mini foxy recently (as she is going overseas). I think shes approx 3 years old. Ironically, I was waiting for this weeks wages to get her spayed but tonight I found neighbours male has dug under my fence (she is on heat since last week) and I found them "in a tangle". Q: Is it possible to get her spade/neutered immediately tomorrow etc even though she is on heat/ and has just "done the tango"? (as I dont want puppies) thanks