you can use ice types or get an action replay code and get a bunch of lvl 100s. simple.
mainly ice
i tryed the same pokemon its really hard your best chance of beating here level up a dragon pokemon with good dragon moves - such as shiny gyardos - until its at least 15 levels higher then her best pokemon thats the only way i beat her and my typhlosion was level 100.
That's entirely up to you
You can't battle against ash.
all you need is lvl 40+ pokemon dragon's good, but ice is best) and put the boulders in the holes. use the walkway they created in the lava, and go beat clair! what seems strange is that they have lava in a kid game (no offense to teenage pokemon players)
Have a good Fire and/or Ground Type...
Of course it can, golbat evolves into crobat if the friendship between it and u is good.
use a good fighting type Pokemon like machoke and use its moves
well i beat the elite four with one Pokemon that was at level 60.
lance is the champion in the johto league, after beating the elite four you will face off against lance.and his Pokemon are really good.
Clair
There really is not a best Pokemon that stands out above the rest. in fact, any Pokemon that is really high lv can kick butt. though legendaries are good for beating the elite four