Any tips for fighting Hilla?

Every time the little helper person announces something, Stop attacking. If its Damage Reflect it always pops up a quarter second before the helper person says something, which will pretty much get you killed every time. All the other times its not too bad, Stay in the pentacle, avoid the tombstones, etc.

Or just time it yourself. I almost never die at Hilla because I time her DRs.

The first DR happens at about 90% HP. Just attack between animations when she reaches around that health.

Subsequent DRs occur every 80 seconds after the last one began. Or if you don't want to calculate 80 seconds, just take the time when her DR ends minus 1 minute.