It's not stealthy just because she's covering her mouth. This image doesn't match the description in the wiki page for stealth_sex.
However, she is doing it while Suwako is there sleeping and thus unaware of what is happening; if Pyonta doesn’t count then it would still match the description.
However, she is doing it while Suwako is there sleeping and thus unaware of what is happening; if Pyonta doesn’t count then it would still match the description.
You're right. She blended into the background so I didn't see that there was a person sleeping there.