I'm sorry for your loss. It sounds like Tessa's end was quick and relatively painless. You need to block out your Mom and the other people who take a mean spirited joy in harassing you. What is important is the love you had for Tessa and she had for you. If ANYONE hassles you then just point out that you neither asked for nor cared about their opinion.
Right now Just give yourself some time to grieve for Tessa and don't pressure yourself to make an instant decision on how to bury her.