I had a girl who did just that "I don't know" phrase all the time.
This is what I did with her, I started saying "I don't know" too alot more times that she would plus right after she would say it.
The reason for this was to point out to her that she was saying this too much & it pissed me off! Doing that worked, she stopped for a month then start doing it again. So I did that again this time she got pissed off with me of copying her.
Next I try to question her to see if it was indecision or that she was hiding something from me. At first it was indecision but one night when she was doing it, I questioned her. She refused to answer then asked for a brake in the relationship. I thought ok
Now a few months late, she comes back to like everything was ok & back to square one. Two weeks after getting back with her she was still doing the same old "IDK" crap, in one chat with her I lost it when say that. I said "You f*****g know, NOW make a bloddy decision!", we had a fight then she told me that she was seeing another bloke behind my back. In the end I got rid of her.
Basically you need to challenge your gf about the issue or end the relationship, for you own insanity.
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