Chiasso? Muchová seems to be still on the list as direct main draw entry, qualies were drawn. I wouldn't count on that being a factor in timing of the eventual withdrawal.Not yet.
What about Muchova in C-Beaubourg? if listed here, she could replace Siniak in QList in case...
Pála (czech captain) said they were talking with all three which are Q list here (Siniakova, Vondrousova, Kr.Pliskova) and that it s a tough situation for the 4th as she might not get to play (with Ka.Pliskova, Kvitova, Strycova on the team), but it would mean the 4th would have to sacrifice the tournament in Stuttgart. Later they announced Siniakova as the 4th player.
( For Siniakova is likely not that much of a big deal as she still has a cushion of two non-countable result of 55 pts each and she doesn't defend anything that week yet )
So I assume it will happen. Although I would be intrigued to see whether it would be at least physically possible to play the qualification (not sure about the rules in such case) as she would be on the spot and likely to play only in doubles if any matches at all.