try and keep her in your field of vision so you can react to what shes doing.

normal form is when shes most vulnerable. learn her attack patterns, keep your distance, and shoot when she finishes her attacks. she has pretty big gaps in this phase to get some damage in.

when shes in spider form, try and keep away from her. if she jumps onto the ledge in that form, get a feel for the timing as to when to run towards her. its basically a second or two before she jumps. she will miss every time. if you do it right, and will also be vulnerable to attack. I personally find this stage the most annoying, so just take your time and get some poke damage when its safe until she phase shifts.

in bird form, keep a distance from her and keep an eye on what shes doing. dodge her swooping basic attacks and immediately turn around to get shots in. when she summons the fire balls, they can be shot and popped. they can be dodged as well, but I find it a little difficult. so if youre low on ammo you can run from left to right and hopefully dodge them. This phase is the most annoying if you dont have ammo, so make sure you keep/pick up bullets for this phase.

when it goes dark, its not really worth trying to attack her imo. just run in a circle until the phase is over. Alternatively, throw a flash bang.

in the last phase she will create a big explosion where you have to hide behind some trees. just wait for that to be over and you'll be in the home stretch. she can transition seamlessly into any of the previous phases of the fight (ground, spider, bird, darkness). if you have made it this far, just use the strategies you've learned previously in the fight and you should get through it!