Hi Lisa, sorry about your dad. I can imagine how upsetting it must be for you and your family.
With regards to your tribute, if your stepmother has a traditional heart (ie white based with spray) I think the heart you did in the gallery is stunning, quite unusual (and would be very different from your stepmothers) and different when using the colours of reds and blue you're thinking of. I'd definately go for an open loose heart.
My thoughts are with you, Jo x