It's unlikely, unless you've managed to be in direct contact with your sister's saliva. Glandular fever, typically, is spread through kissing (but you could probably get it if she sneezed right in your face or if you've been sharing cutlery/cups/mugs without washing them first). I had glandular fever earlier this year, not entirely sure how I even caught it in the first place. Most people have already had the virus when they're very young and it just comes out as a cold rather than full blown glandular fever, and it rarely strikes a second time. So the likelihood is you'll be fine!