Happy birthday to her!

My granny is 88 and we often go to the theatre together, she's a great companion. 

Hi. That is awesome! I can't imagine myself at 70. I always wonder what I would look like or will I be able to move around on my own. Have you ever thought about it?

Best regards,

Teacher Keevan

In the United States, the word "anniversary" is used for 

1) Wedding anniversaries, and

2) Anniversaries of historical events.

Birthdays are simply called birthdays, not "anniversaries."

For example:

"They are celebrating their 25th anniversary. The 25th anniversary is traditionally the silver anniversary, so he bought her a new set of silverware (knives, forks, and spoons). Of course they got stainless steel, not real sterling silver."

"In 2016, Wellesley College celebrated its 100th anniversary. It was founded in 1916. The theme was 'One hundred years of women helping women.'"

Congratulations to your grandmother. 70 can be a wonderful age to be, and being a grandparent has been wonderful for me. 

Happy Birthday, Granny. I spend my teenage years with my grandmother. Grandparents are the absolute best.

Not really but I do really take care of my skin and my health so hopefully I will be healthy and young at heart.