First, one of the most important aspects of community leadership is ensuring ongoing leadership by recruiting and fostering other leaders.
So, only knowing what you said about the original organizer, she was obviously a great doer, but maybe not providing as much vision as a leader.
For many communities, especially small ones, a "do-ocracy" applies. Those who spend their energy on topics, and can influence others to do the same, determine the direction of a community.
Your community isn't dissipating because you lost her influence. Its dissipating because it lost its doers.
This is a good time to assess what you what you like about this community, and why you are still around and worrying about its future. If you are inspired by the same vision she had, awesome! Obviously others are. If there are other directions you would take it, then do something with the community in that direction.
My only additional suggestion is, see if you can get others to join you in the doing. Ask other people to manage or handle aspects of either the community management or the activities related to its purpose. Community management would be items such as recruiting, communication, and administration. Activities related to purpose are the reasons why people come together to do things in this community, whatever it may be.
I presume the purpose is what inspires you to be in this group, so focus on the activities. Ask others to help with the management aspects. If the activities related to your purpose are taxing for a single organizer to achieve, then try to get others to help you.
You needn't worry about trying to replace her. In fact, you can even try things such as virtual presence like Google Hangouts and ask her to join your community from afar as an ongoing mentor, alumni, or inspirational leader.
Hopefully this helps you some.
A doer is what birthed your community, and what it needs to thrive again. This time, try to get more people to replace the one. That's how amazing she was.