Your aim needs work, some easy shots were missed so I'd suggest practicing. Maybe go into the practice range where the enemy bots move and shoot from the highground and practice using scope and unscoped.

Your positioning needs work, you don't go for highground and play aggressive as seen by you being in Reins face then getting charged towards the start of the match. Try to watch some Ana players on twitch to get a rough idea on their positioning.

Like at 4:04 you're frontlining as Ana... you got no mobility and you're lucky you aren't always being punished for this. Ana heals the team by shooting her team and you can't get a good view of your team and who needs healing from the frontline. Try to play in the backline a bit more so you can see if someone needs healing cause if they need heals and don't get them then they're an easy target for a flanker.

Some Ana players avoid going on highground because they don't have confidence in being able to hit shots from far away so practice your aim and that will hopefully enable you to heal from a safe spot and not just shooting bullets into your Rein's ass.

Lastly your nade usage is... decent but I feel like you use it in weird moments. It's good to use it on a team member when they're low and taking a lot of damage since it increases how much healing they get but it's also strong against enemy targets mainly large groups since it stops them from healing. Lower ranks don't tend to take advantage of a group of enemy targets hit with an Ana nade but I feel like you use it when you're missing shots and are frustrated and just go the easy way out and hit E.

Couldn't watch all of the VOD since it's late and that but hopefully whatever I typed is of some use and good luck with the climb.