To me it is just too cliched that the experience of true love changed the female changeling's mind.
It is a bit, or at least it could be if it were overdone, which is probably why the writers chose the understated approach. The whole Kira/Odo/Female changeling love triangle had its cheesy side, but it was a pretty major part of the show through seven seasons.
The Changelings have been around solids in the Gamma quadrant for centuries, I think they probably have a keen understanding of the ways of solids.
I don't think they do. The female changeling experienced "solid intimacy " for the first time with Odo in season 6.
Their agenda has been one of conquering worlds for a very long time and they have built whole races for this purpose. I don't think it was ever clearly shown why they are conquerors, surely it can't all be out of fear?
Well, the stories of the changelings' persecution at the hands of solids is given as the motivation for the Founder's secrecy and militant approach. They also seem to have a desire for order, though, as another motivating factor.
I think it would be very twee for a revelation of looooove to change all that.
I don't think it necessarily would, but it could certainly be enough to change the female changeling's mind on this occasion. As for the link, that is another issue, but it is certainly one of the reasons why Odo returns: he needs to share what he has learned, as was the stated purpose for sending the 100 out into the galaxy in the first place.
And anyway, I wouldn't describe Odo and Kira's relationship as clichéd exactly, at least not as expressed in season seven episodes such as Chimera. It's about love transcending barriers such as prejudice, superficial appearance, and even physical form.