Professor expressed interest in working together, is not responding to emails? Recently I received contact info for a professor close to me, with similar interests (Professor B), from another professor I have a long-standing working relationship with (Professor A).

I spoke with her at the beginning of the month, and had what I thought to be a great call.  She expressed interest in having me work with her on an upcoming grant remotely, in preparation for applying to her graduate program in the upcoming application cycle.  We ended the call with the decision to have me touch base with her in a week, when she would know more about her grant.

The next week, I sent her an email to follow-up, and set up a call to talk more about the project and set up time to visit her lab (something we discussed on the call.  No response for one week.

I sent another email, and received a one sentence response: "Things are hectic now, please touch base in a few days".  I waited 4 days and sent another short message.  It has now been a few days and I still haven't gotten a response.

What are my best next steps?  Should I write this lead off, and not bother sending anymore emails if I don't hear back?

EDIT: That is to say, how long should I wait for a response before reaching out again?  I don't want to be bothersome, but I also don't want too much time to elapse and this project to possibly be scrapped or forgotten.  

I also have the option of going to Professor A and starting some work on the project while Professor B is otherwise occupied.  But at the same time, I don't want to seem like I'm "going around" or otherwise excluding Professor B.
It's normal for professors to be extremely busy for an extended period, and not be able to respond to anything that requires significant thought or planning.  I would not say that she is "ignoring" your emails.

I would wait about a week from your last message, and then send one more message with a deadline.


  Dear Professor B,
  
  Just wanted to touch base again regarding my application and our discussion about working on Project X.  I am trying to make plans for the next few months, so if we are going to move ahead on this, I would need to know by date MM/DD.  I really hope it works out and look forward to hearing from you soon.


After that, do not send any further messages unless you get a substantive response from her.  If you don't get a response by the deadline, move on and look for other opportunities; either she isn't interested, or she hasn't been able to make time to evaluate your request, which would itself be an indication that she wouldn't be easy to work with.