Spaying during heat cycle?

Personally I would wait until she's finished her season. At the earliest have her done 4 weeks from when she first commenced bleeding ( as you might know the bleeding stage isn't actually the fertile in season stage...although some dogs will bleed during the whole heat cycle which is around 21 days or so). I'm not an expert on breeding by any means ( the vet I worked with was though). We would never spay a dog if it was in season or at least strongly advise against it. Yes it can be done but there is a much greater blood supply to the uterus and associated blood vessels which leads to a higher risk of bleeding/haemorrage during or after the surgery. Plus the tissues are more fragile to handle when you are operating as everything is engorged and enlarged.
Of course if you can't have it done any other time then do it now rather than not at all but be aware there is a slightly higher risk with the op. She probably won't have her next season for another 6 months so you've got a couple of months to organise it and do it at the safest time possible for them.