I have a grandmother whom I have started to help to pray recently. Given that she cannot get up on her own and that moving is difficult for her, she performs Tayammum (dry ablution). I was not aware of this fact and let her pray without it at first. Does she have to repeat those prayers? Understand that she was not really practising before and that explaining this to her would be difficult. I have to help her do Tayammum and then she prays lying down. I accidentally crossed her lying figure once while she was in prayer to reach for something across the bed. Does she have to repeat that prayer too?

All perfect praise be to Allah, the Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad is His slave and Messenger.

Your grandmother is obliged to do what she can. If she can perform ablution, then she must do that, otherwise she may perform Tayammum and then pray.

If she is able to pray while standing, then she must perform the prayer while standing, otherwise she may pray while sitting if she can, or while lying on her side.

If she does what she is able to do, then her prayer is valid, but if she is negligent in doing what she is obliged to do, then her prayer is invalid.

Hence, you should order her to do what she is obliged to do. If she has left a condition or a pillar of the conditions and pillars of the prayer because she was unaware that that it is an obligation, then she does not have to repeat the prayers (that she prayed in this way) according to Shaykh Ibn Taymiyyah and those who agreed with him in this opinion.

It is permissible for you to follow this view due to the hardship that your grandmother will find in repeating the prayer, and her prayer is not invalidated by you passing in front of her, according to the view of the majority of the scholars.

Allah knows best.