Is there something psychologically wrong with my grandmother?

Okay, im 13, she's 76. I went to bath and body works and got myself a ceramic strawberry candle holder, and a few candles to go in it. I left it downstairs... and i come back because i woke upp... it was gone... my grandma had thrown away my mountain dew when i deliberately told her not to throw it away. and she said clearly okay. then, she said later on when i was looking for it " i throw it away, you didn't tell me not to throw away your bottle " when i KNOW i did. Then when i was looking for my candle, ceramic jar, and the lighter, she told me flat out, she doesnt have it in her room. But I smelled my candle in her room. I went back upstairs. I snuck downstairs, i heard her close my ceramic jar. And i saw her taking out the lighter and putting it back in the drawer where she said it was, and made me look for it for about 5 minutes. I confronted her, and she said it was in there. I was like omg with a serious face. I was pissed because i knew for a fact shhe was lying. then my mom came downstairs, and my grandma told my mom, i have the lighter in my room because i took it and her candle ceramic.... like why are you going to lie to me, when all i needed was that because i like taking baths with a candle lit. Is there a psychological problem that has to do with hiding things, and lying? if so... waht's it called? I really need to know, because im getting tired of this. she does this all the time.. i've been putting up with this for like 3 years now, and i am sick of it. she also has a problem of explaining all of her problems to random strangers... what is that called? im soo aggravated... i got my candle back though..