How did Bella follow Cissy?

[pippin_999]

No: HPFGUIDX 144450

There doesn't seem to be a way to track a Disapparated person. The Ministry
can't follow the Death Eaters who Disapparate at the World Cup. Tonks tells
Harry there's no point in yelling at Mundungus because he'll probably be in 
London by now. Harry knows there's no way to catch up with Snape and the
other DE's once they've Disapparated.

Now,  according to the Ministry's Apparation instructor, you have to have your
destination clearly in mind to Apparate successfully. Bella
had never been to Spinner's End before and  Narcissa acts as though she 
didn't want Bella along.  

How did Bella learn where she was going?

Was Narcissa's thought read against her will before she Apparated? 
Did Cissy "leak" the information because she already intended to ask 
Snape to take the vow? 

Any other ideas?

Pippin