Wow! She is an incredibly cute baby. I don't just say things like that, either.
Was she born a little early? Sometimes kids who are born early take a little longer to reach those milestones. She looks happy and healthy.
Oh, also, some kids skip steps (for example, never roll over, but just go straight to crawling). Despite what some people will tell you, this is not harmful at all. She will do what interests her the most. If she is pulling herself up with help, she seems right on target in terms of strength and coordination, from what I remember reading. It sounds like you're doing a great job providing her with opportunities to get moving, too. 
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The machine does not isolate man from the great problems of nature but plunges him more deeply into them. -Antoine de Saint Exupéry