Yes, during a judicial campaign, candidates for judicial office may attend political gatherings.
CJC Canon 7(A)(2).

If Judge Bell is unable to attend, may she ask another judge to speak on her behalf?

Yes, CJC Canon 7(A)(2) permits a judge to speak on behalf of another judicial candidate. The judge who will be speaking on Judge Bell's behalf does not need to be a candidate to attend the political gathering.