First off, stop trying so hard with the in-law. It could be that she is genuinely busy, but, if she's blowing you off, she's genuinely not interested. This stinks, but it's not a big deal. At this age your little girl has no idea what "Grandmother" even is, and, with the amount of children now-a-days who don't even know who daddy is, she's already ahead of the race. If you need the figure of an elderly, motherly/grandmotherly persona, there are several ways to fill that void. One, go to church. I know it sounds like I am a religious nut, but the fact is that older people tend to go to church, many of them who would just love a little child to "play grandma" to for a few hours. There is also the "adopt the elderly" program where you can visit someone who can become this "grandparent".
Second, and don't take this the wrong way, are you, perhaps, more interested in filling your own void that was left by your mother's passing? It's hard when you're thinking "Oh, if only my mom could be here to cuddle my child," and it's extremely easy to convert those wistful felings into guilt that, perhaps, your child is not getting enough attention. If you're concerned there, and you're making efforts, then she already has someone to fill her with love - YOU! Relax, love your little girl, and forget about the people who are being "worthless".