Lactating queen in heat cycle?

My queen (foster from the shelter) delivered 4 kittens 6 weeks ago and last week she went into heat. She is wild and will cry, dig in the carpet to get out of the door and yowls constantly. She will nurse briefly, then jump up and dump her kittens to start yowling.

The shelter is having her spayed tomorrow as the kittens are eating well on their own and mom was taken away from the kittens last week to reduce the lactation.

I have the option of bringing her back and allowing the kittens to nurse or leaving her at the shelter for adoption.

I am concerned with the nursing after spaying. It could be painful for the queen.

Any suggestions how to ease her discomfort, or should I just not bring her back?

Kittens are doing well with eating, litter box, bathing and socialization (I now have them underfoot) They all weigh about 2 pounds.

What have other people done when the mother cat goes into heat????

Thanks