is my sister right about not telling me the truth or am i over reacting?

my sister has 4 children ages 8-17. I have 2 13 and 15. both families are fairly close. we get together at my moms every 3rd sunday. my daughter had a birthday (13th) and i asked my sister if if her 2 girls could spend the night(8 and 15) I asked her in person, she said let me look at my calander. Days went by so I texted her about that and a few other things. She answered and responded to the other things but not the birthday sleepover. I texted her again and this time no response. Several days went by and i texted her again...this time i said " Listen you need to tell me what is going on everytime I ask the girls over you say NO what is really going on." she responded in a 6 text reply...one girl had VBS and the other may do volley ball she wasn't sure...then she said even if we could figure out the logistics of it all could she be very honest with me and say she doesn't feel comfortable with her girls at my house. She then said if you want to know why I would be glad to talk in person. I immediatly called her and of course she would not answer. A few days later she texted and said lets meet for hot coco and talk. So we did, she made small talk for about 10 minutes and then I said ok what is going on?? She said I just feel uncomfortable with them at your house. I responded WHAT!!! and she said "IT'S JUST A MOTHERS INTUITION!" I still don't understand ...(this is August) I said your whole family was over for the 4th of July there was no problem. she said well then mom and dad and herself were there to protect them. she repeated herself again and i walked out really hurt and mad. A few days later my mom called and asked if we could all sit down and talk, I told her I would but I wanted the TRUTH from my sister. We went to Steak and Shake (my mom, my little sis and my older sister) (the older is the one with the problem) anyway she said she never said she had an intution she just feels they wouldn't be safe at my house. WHY!!! my mom asked me if I could see my sisters point and I said NO. It's been 2 1/2 months and I still san not understand or see her point. she has not spoken to me nor I to her (I wouldn't want her to feel incomfortable) My family have refrained from going to my mothers on the 3rd Sunday. and Thanksgiving and Christmas are coming up. My older sister has always been over critical and "better" than me. this is not the first time we havn't seen eye to eye, but usually I suck it up and say I am sorry wether I am or not... just to keep the peace. Not this time I am hurt and angry. what do i do