First, state an honest observation. "Constantly" is a word like "always" and "never." She texts more than you are used to. You think it's rude because ... it interrupts your time with her? She ignores you when you thought you were doing something together?
Next, try telling yourself some corny "I" messages.
"When dinner is interrupted by texts, I feel frustrated because I was wanting attention and respect."
"When I notice texts happening for long periods, multiple times throughout the day, I feel sad because I want to matter more, to be in on the fun."
Figure out what the real feelings and needs are. If you just think what she's doing is stupid, well, don't be so judgmental.
But if you have needs that aren't being met, and a concrete request for change could help them be met, then you can ask for what you want.
"Hey, I would really like some exclusive attention around dinner time, and for a couple of hours every evening. Would you be willing to put your texts on Do Not Disturb from 5-8, and let BF know we are gonna keep this time to ourselves? Could we try that for a week, and see how it goes?" (Using whatever reasons and ideas for limits --time, place, or activity-- that make sense to you)
She may agree. She may not. You may prefer to be more vague and ask how you can get [whatever it is you are needing] without infringing on her communication needs with BF. But ultimately you have to figure out what you're needing out of her texting less, because her texting less won't necessarily get you what you're needing (unless it's to control her level of texting, which doesn't seem like a reasonable need). And you will have to negotiate with her around getting it, whether through agreements about texting, or some other way.
Are they in the throes of NRE, or is this an established relationship? Not that NRE would negate your experience, just that knowing it's a temporary thing might help you weather it.
