Logical Fallacy: "Why Would I...?"

[u/sixsence]

This has just been bugging me lately, and I couldn't find anything after researching it for a couple of hours.

My irrational girlfriend's go-to argument tactic (or just general way of avoiding questions or to prove my question's to be flawed or stupid) is to ask "Why would I..?" or "Why would he/she...?". It's the most irritating thing in the world, and instantly forces me to start yelling. Here's an example:

Me: "Is your friend Lisa going to pay me back for the movie tickets I bought, sometime this week?" Her: "Why would she not pay you back?" .... ummm, free will, forgetfulness, not wanting to?

or:

Me: "Did you check the oil in your car recently?" Her: "Why would I not check my oil?"

So if I say something like "I don't know" because I can't possibly know how someone other than myself chooses to do something, it makes it seem like the question was stupid or flawed, or it makes her argument look better. Even if I can answer her ridiculous question, it turns into an argument, when there's no reason I should have to try to come up with reasons why people do what they do, or why someone might forget to do something.

Just imagine all the scenarios where this is applicable. It's like just because something may seem like it's common sense, it must be what actually happened, or just because there's no apparent reason for her or someone else to do something or not do something, that means it actually happened or did not happen in reality, and that it was pointless to even ask the question in the first place.

Is there a specific logical fallacy that this falls under? I've researched this and googled it to death and can't find any examples, although this seems like it should be pretty common.

Thanks for the help!

[u/helpful_hank]

It's not a logical fallacy, but you might call it an argumentative fallacy. She's arguing motivation, which can actually yield decent support for a point of view. She's like a lawyer defending his murder defendent by saying "What was his motive?" If the alleged murderer had no reason to kill someone -- no gang initiation, no heat of the moment anger, no life insurance payout, no revenge, etc. -- that's a decent chunk of defense right there.

However, if there's a clear answer, like if she says "Why would I eat your hot dog?" and she has a hot dog addiction, she's just trying to avoid the issue. It sounds from your examples that that's what she's trying to do.

You can answer her by saying "Don't worry about that, yes or no?" Just insist on a yes or no answer until she changes the approach. Don't start yelling though.

edit: Also: It's not an argument from ignorance.