Why do I feel guilty for helping out? 😩

My sil gave birth 2 days ago. From the beginning my mil said she was going to push her to breastfeed, the thing is my sil has flat/ inverted nipples and her baby isn’t latching correctly. They gave her a latch assist at the hospital which was helping her but now she’s at home and I guess she’s having a hard time feeding him. Now the thing is I had 2 breast pumps 1 I bought and 1 I received so I decided to give her one. A few minutes ago my mil called my husband because she was trying to help my sil set up the pump and they couldn’t figure it out. Keep in mind that I had already set it up for her all she had to do was connect the suction to the bottles and plug in the pump. So I told my husband the manual was in one of the side pockets of the bag and my mil got upset and said “I don’t know how to use this pump I know how to use the other pump she has, idk why she didn’t give her the other one.” She was referring to the pump that I had bought. Now the thing is I really don’t wanna give her the other pump because I know I won’t get it back, so am I in the wrong? I would have also thought my sil would have tried it out before the baby got here just so she can know how to use it but I just feel guilty because I tried to help out and they ended up getting mad.