Is the coherent white substance that adheres to the vulva, which is difficult to remove and causes great hardship before every prayer, ritually impure, and must it be removed?

These secretions are either pre-seminal fluid (madhy), post-urination fluid (wady), or vaginal discharge, and each has its own ruling.

If it is discharged upon arousal, it is pre-seminal fluid (madhy). If it is discharged after urination, it is post-urination fluid (wady).

If there is no specific indicator, then it is vaginal discharge. This is pure (tahir) and does not require ritual washing (istinja) nor washing what it has touched on the body or clothes, but it does invalidate ablution (wudu).

If its discharge is continuous, then your ruling is that of someone afflicted with incontinence (sals). You should perform ablution for each prayer after its time has begun, and pray with this ablution the obligatory prayer and whatever supererogatory prayers you wish until that time expires.