Wife gives spontaneous short BJs but then stops without a finish

Me and my wife have 3 kids so we have sex when we can but in a perfect world we'd have more. Now I'm not complaining about that, I'm perfectly happy. HOWEVER..

My wife has recently clocked on that due to "life" my sex drive is higher than hers and she's started to spontaneously give me the odd 15 second blowjob when she's noticed I'm erect. But this for obvious reasons is leaving me hanging and putting me in a position where I want more but don't want to push or mither my wife. I'd rather her not do it than to start and pretty much immediately finish but I know in her eyes she's doing it as a treat so I don't want to upset her.

Does anyone have any advice on what I should do in this situation? It doesn't feel right to finish myself off in these moments but I don't want to make her be a part of anything she isn't in the mood for. I've considered asking her to do it for longer so I can finish or to atleast be with me whilst I finish myself but I don't want it to feel like a chore for her.

She's just gone off to bed and has told me she might wake me up with a quick 10 second BJ in the morning and it's left me not knowing how to feel about it all.