This is a pretty good example of the limitations of automated grammar/spelling checkers. Especially for poetry, there are many usages that they simply aren't designed to handle.
Here, though, Grammarly is half-right. It's true that "Beauty rose" would make a fair amount of sense. But it doesn't say the same thing "Beauty risen" can. Using the past simple here is good if you want to describe an event, something that happened, focusing on actions.
But if you want to describe an aspect of a person, a description of them, that's not what you want at all. The past participle can be used as an adjectival phrase, describing the girl you're talking about, rather than mentioning something she did at some point.
If you want to do this, though, the period at the end of the first line quoted needs to be a comma: that line by itself is just a description of a person and the sentence needs to do something with that to avoid being a sentence fragment. (In this case, the second line refers back to the first with "you".)