IMO she's being snotty because, maybe, it tickles. But regardless, she IS kicking out and that's dangerous. I had similar trouble with my mare but rather than kicking, if she even saw you reach for the spray bottle she'd practically run backwards from you. Dunno why she became so afraid of it, but all I did was follow her and stay calm and she got over it. Your mare doesn't look afraid, just rather annoyed. Having said that, she should have enough respect for you to stand regardless. She's not kicking at the spray, she's kicking out to tell you she's annoyed, and she's going to escalate to kicking out whenever anything annoys her. Shouldn't be tolerated, but again that's my opinion. I'd say a snap down on the halter and a firm "Stand." or whoa, whatever you use to make her be still. Maybe not a smack, but if she respects the halter, demand she stands still.