A little bit like the Sage moment but perhaps because it's Bella it will be better thought out, she's not one to mince words so coming from her it could be something like "I haven't been myself lately because i've fell in love with you" or something along those lines
Like you say a genuine declaration is much better and to be fair, none so far have been accidental, MC has told 3 of them he loves them without hesitation, In Josy's case she barely let him finish before saying it back

Bella just being the maturest I could see it maybe going differently, she knows the power behind those words and she's been down this road before, I think we theoried in the past that if MC says it first she might not say it back immediately and will think on it, a confession from her first would be special though