Monopoly Deal Just Say No
Assuming Player B could play Just Say No in that situation, it will be legal for Player C.  However, this is a big assumption.
The problem is that you have waded into the extreme grey area of Monopoly Deal rules.  Monopoly deal has a woefully incomplete rules framework and is missing the all-important official Errata and FAQ document.  monopolydealrules.com has many opinions on the game and how it should be played, but has the double downside of being nether official nor definitive.
So let's dig into how Just Say No works in general, with what precious little we have to go on.  The text of the card is:

Just Say No!  Use any time when an action card is played against you.  Play into the center to use.

There is also the &quot;Cards in more detail&quot; section of the rulebook, which says

Just Say No:
Use this card at any time to cancel the effect when another player plays any action card against you.  If that player has another Just Say No card, they can use it to cancel yours... sorry!

The rules clarification is helpful, because it means that Just Say No cancels the whole card and not just the aspect of the card that harms you.  The remaining question is what types of cards can be affected by Just Say No.
There are two possible readings:

&quot;Played against you&quot; is read strictly as cards that affect one player in particular.  To put that in Magic the Gathering terms, a card must target one player or a card belonging to that player in order to be eligible for Just Say No (i.e. Just Say No is the equivalent of Rebuff the Wicked).  This means Just Say No only works on any-color Rent cards (because they target one player), Deal Breaker, Sly Deal, Debt Collector, Deal Breaker, and Just Say No itself.

We take the looser definition of &quot;played against you&quot; to mean Just Say No can be used on any card that directly affects you negatively, thus adding the following to the list of valid targets: It's My Birthday and 2-color Rent cards.


In the case of interpretation 1, your question is moot because Just Say No can't be played on a 2-color Rent card.
In the case of interpretation 2, there is nothing preventing multiple people from playing Just Say No on the same card.  If the first Just Say No was negated by one from the original player, than anyone (including player B in your example) could play another one to try to negate the original card.
My play group uses interpretation 1.  monopolydealrules.com suggests interpretation 2.