Respond when she's clearly not interested in casual hangouts

Annoyance at a casual invite usually means she either thinks you're not serious about spending time with her, or she literally doesn't want undefined hangouts. The second is just her preference. The first is about how your invitation landed. A vague 'grab drinks sometime' requires her to make it a real plan, which feels like you're asking her to do the work. That gets old. She's signaling that if you want to see her, you need to actually decide on something and ask her to join it. Time, place, activity. Real plan.

Your reply needs to show you heard her and can move the ball forward. If you still want to see her, pick a specific plan and invite her to that. Not 'what would you like to do,' but 'I'm going to this place Friday at 7, come with me.' That's the move. It signals that you want her specifically and you're willing to put thought into it. If you actually can't commit to something specific right now, or you realize you two just want different things, then be honest about that instead of pushing. Either choice works. She'll respect both more than pretending this didn't happen.

Reply within a day or so. Letting it sit makes it awkward. If you're going to shift to a real plan, do it while the conversation is still fresh. If you're going to step back, do that too. Waiting three days and then sending a casual invite again will just confirm her original read. If she doesn't respond to a solid offer, you've got your answer. Don't follow up twice. One real plan, and if that doesn't land, you're done here. Respect her boundary and move on.