Can a custodial parent veto a court ordered visitation schedule of her own accord?

My ex wife challenged me today when I was picking up our children for my visitation. I had been gone for about a year since seeing my children and brought my mother along so the children would see a familiar face. In just the last few visits it seems as though I never left and my kids are having a great time with me. I had my day in California Court a few weeks ago and asked the courts to define "reasonable visitation" (btw- if you are going through this, NEVER agree to reasonable visitation without definition). It leaves the sole decision of visitation to the mothers discretion. Anyway, I went to pick up my children today and the court order clearly states that I have to be present for pick ups and drop offs. I did not bring my mother this time and an explosion of animosity from my ex wife ensued. She then skulked about and said there was nothing she could do about it right now but a flood of sms text was soon to come. Now she says that visitation begins and ends at pick up and drop off and I need to have my mother present even though the order does not specifically say this. Can she veto the courts decision and what action should I take if she does? This woman has endless animosity towards me and I now see that her prior argument of "in the kids best interest" is false and anything she can do to hurt me is what really counts.