If Ross saw her there then surely he would’ve seen someone else there. So either he did actually see her jump or he saw who pushed her and is covering as he thought she deserved it - thats if they aren’t being predictable in making it him.
But when she fell it didn’t look like she’d been pushed. It looked more like she’d just let herself fall. There was no panic in her face like there would be if someone pushed you. So I’m still thinking she did just top herself and they’re making a whole thing out of someone pushing her. The letter will probably turn up to show she was about to commit suicide so the police may change their theory and we’ll find out that the marks on her arms were from someone (Ross?) actually trying to stop her jumping not from shoving her over the edge. That’s my theory at the moment - it’s subject to change
Also the scratches they found on her from a few days before could’ve possibly been from her scuffle with Gabby maybe?